Transient equivalent heat source simulation method and system for static induction heating of thin plate

Abstract

The invention discloses a transient equivalent heat source simulation method and system for thin plate static induction heating, and the method comprises the steps: building a space rectangular coordinate system and a corresponding electromagnetic-thermal transient bidirectional coupling simulation model according to the actual working condition of thin plate static induction heating; calculating to obtain heat generation rate transient spatial distribution under the spatial rectangular coordinate system, and fitting to obtain a heat generation rate transient spatial distribution function; and establishing a local rectangular coordinate system at each heating position of the to-be-processed thin plate, applying the heat generation rate transient spatial distribution function to each local rectangular coordinate system, and performing heat-structure coupling calculation to realize deformation prediction of the large thin plate component. According to the method, the equivalent heat source simulation analysis model for static induction heating of the thin plate can be accurately established, accurate prediction calculation of the thin plate induction heating forming machining process is rapidly achieved, and the time needed by simulation calculation and the modeling complexity are effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of metal hot working simulation, and specifically to a transient equivalent heat source simulation method and system for stationary induction heating of thin plates. Background Art

[0002] The stationary electromagnetic induction heating process is widely used in the controllable hot forming of metal thin plate components, such as curved plate bending and deck leveling in the shipbuilding field. To improve construction efficiency, it is necessary to predict and calculate the induction heating effect. The electromagnetic-thermal-structural coupling method can accurately describe the induction heating process, but its modeling is difficult and the calculation takes a long time. The traditional equivalent heat source method uses a constant heat generation rate spatial distribution function to replace the complex electromagnetic heat generation calculation. Its advantage is that the calculation time is short, but its parameter setting depends on experience and it cannot accurately describe the complex transient process of induction heating. Therefore, it is necessary to accurately simulate and analyze the transient equivalent heat source of stationary induction heating. Summary of the Invention

[0003] Aiming at the problem that the existing equivalent heat source simulation method for induction heating cannot accurately describe the significant change of the spatial distribution of the heat generation rate inside the thin plate with time during stationary induction heating, the present invention proposes a transient equivalent heat source simulation method and system for stationary induction heating of thin plates, which can accurately establish an equivalent heat source simulation analysis model for stationary induction heating of thin plates, quickly realize the accurate prediction and calculation of the induction heating forming process of thin plates, effectively reduce the time required for simulation calculation and the modeling complexity, and has important engineering application value and obvious economic benefits.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a transient equivalent heat source simulation method for stationary induction heating of thin plates. According to the actual working conditions of stationary induction heating of thin plates, a spatial rectangular coordinate system and a corresponding electromagnetic-thermal transient two-way coupling simulation model are established, and then the transient spatial distribution of the heat generation rate in this spatial rectangular coordinate system is calculated and the transient spatial distribution function of the heat generation rate is fitted; then a local rectangular coordinate system is established at each heating position of the thin plate to be processed, and the transient spatial distribution function of the heat generation rate is applied to each local rectangular coordinate system and thermal-structural coupling calculation is carried out to realize the deformation prediction of large thin plate components.

[0006] The spatial rectangular coordinate system mentioned above refers to: taking the geometric center of the coil as the origin of the coordinate system, defining the direction parallel to the upper surface of the thin plate and along the length direction of the coil as the x direction of the coordinate system, defining the direction parallel to the upper surface of the thin plate and along the width direction of the coil as the y direction of the coordinate system, and defining the direction perpendicular to the upper surface of the thin plate and outward as the z direction of the coordinate system.

[0007] The described electromagnetic-thermal transient bidirectional coupling simulation model is established through finite element analysis software, specifically including:

[0008] a) Establish a geometric model of stationary induction heating of a thin plate including an induction coil, a thin metal plate, and an air gap;

[0009] b) Input the electromagnetic and thermal performance parameters of the thin metal plate that vary with temperature;

[0010] c) Input the thermal convection, thermal radiation boundary conditions and alternating current parameters in the coil that conform to the actual working conditions;

[0011] d) Starting from the initial heating moment, for each calculation time step, first calculate the spatial distribution of the electromagnetic field within this time step through Maxwell's equations. After calculating the induced current distribution within the thin metal plate, calculate the spatial distribution of the heat generation rate corresponding to the induced current distribution through Joule's law, and calculate the current temperature distribution of the thin metal plate through heat transfer formulas;

[0012] e) According to the temperature distribution calculated in step d, update the material parameters of the thin metal plate after the temperature change for use in the calculation of the next calculation time step; loop through steps d - e until the target heating time is reached, and finally obtain the transient spatial distribution of the heat generation rate during the heating period for stationary induction heating of the thin plate.

[0013] The described transient spatial distribution of the heat generation rate refers to: the Joule heat generated per unit volume within the thin metal plate due to the induced current per unit time, with the unit of W / m 3 .

[0014] The transient spatial distribution function of the heat generation rate q(x, y, z, t) = q center (t) × f(x, t) × g(y, t) × h(z, t), where: q center (t) is the transient heat generation rate calculated at the surface of the thin plate directly below the center of the coil in the described electromagnetic-thermal transient bidirectional coupling simulation model, and it is an interpolation function with time as the independent variable; the distribution function of the heat generation rate in the x direction The distribution function of the heat generation rate in the y direction The distribution function of the heat generation rate in the z direction where: x, y, z are the coordinates in the described rectangular coordinate system, σ l (t), l(t) is the shape parameter in the length direction of the coil, σ w (t), w(t) is the shape parameter in the width direction of the coil, σ d (t) is the heating penetration depth parameter, t is the time, and the above shape parameters are all interpolation functions with time as the independent variable, obtained by fitting the transient spatial distribution data of the heat generation rate in the electromagnetic-thermal bidirectional coupling simulation model.

[0015] The local rectangular coordinate system established at each heating position of the large thin plate member means: taking the geometric center of the coil during heating at this position as the origin of the coordinate system, defining the direction parallel to the upper surface of the thin plate and along the length direction of the coil as the x-direction of the coordinate system, defining the direction parallel to the upper surface of the thin plate and along the width direction of the coil as the y-direction of the coordinate system, and defining the direction perpendicular to the upper surface of the thin plate and outward as the z-direction of the coordinate system.

[0016] The present invention relates to a system for implementing the above method, including: an electromagnetic-thermal transient bidirectional coupling calculation unit, a heat generation rate data extraction unit, a heat generation rate spatial distribution function fitting unit, and an equivalent heat source model application unit, where: the electromagnetic-thermal transient bidirectional coupling calculation unit establishes an electromagnetic-thermal transient bidirectional coupling calculation model according to the electromagnetic induction heating process of the actual metal thin plate and performs simulation calculations; the heat generation rate data extraction unit extracts the transient spatial distribution data of the heat generation rate in the metal thin plate according to the electromagnetic-thermal transient bidirectional coupling calculation results; the heat generation rate spatial distribution function fitting unit obtains the transient spatial distribution function of the heat generation rate by means of data fitting according to the extracted transient spatial distribution data of the heat generation rate; the equivalent heat source model application unit establishes a corresponding local rectangular coordinate system according to the heating position of the induction heating process of the large thin plate member, and applies the transient spatial distribution function of the heat generation rate on the corresponding local rectangular coordinate system according to the construction sequence. Technical effects

[0017] In the present invention, all parameters of the transient spatial distribution function of the heat generation rate in the equivalent heat source simulation method are directly and simply calculated by the electromagnetic-thermal transient bidirectional coupling model, and each parameter changes with time during the heating process. Compared with the prior art, the present invention can accurately generate an equivalent heat source model and perform simulation calculations for working conditions under different heating parameters, and significantly improves the simulation accuracy compared with the traditional equivalent heat source simulation method without increasing the calculation time consumption of the equivalent heat source simulation method. Description of the drawings

[0018] Figure 1 It is a flow chart of the present invention;

[0019] Figure 2 It is a geometric modeling diagram of the electromagnetic-thermal transient bidirectional coupling simulation in the embodiment;

[0020] In the figure: 1 is a metal thin plate with dimensions of 300 mm × 200 mm × 6 mm, 2 is an L-shaped coil with a bottom length of 200 mm and a width of 20 mm, and 3 is an air domain;

[0021] Figure 3 It is a flow chart of the electromagnetic-thermal transient bidirectional coupling simulation;

[0022] Figure 4Transient variation diagram of the heat generation rate at the center of induction heating obtained by coupling calculation for the embodiment;

[0023] Figure 5 Transient variation curve diagram of the heat generation rate distribution along the x-axis, y-axis, and z-axis obtained by coupling calculation for the embodiment;

[0024] Figure 6 σ l (t), l(t), σ w (t), w(t), σ d (t) parameter transient variation curve diagram;

[0025] Figure 7 Temperature curve comparison diagram obtained from the experimental temperature measurement data, electromagnetic-thermal transient two-way coupling simulation results, and equivalent heat source simulation results of the corresponding process parameters for the embodiment;

[0026] Figure 8 Schematic diagram of applying multiple equivalent heat sources to a large thin plate component for the embodiment. Detailed implementation method

[0027] As Figure 1 shown, this embodiment relates to a transient equivalent heat source simulation method for stationary induction heating of thin plates, including:

[0028] Step 1: Establish an electromagnetic-thermal transient two-way coupling simulation calculation geometric model as Figure 2 shown, specifically including:

[0029] 1.1 The size of the metal thin plate to be heated is 300mm×200mm×6mm, and the material is AH36 steel;

[0030] 1.2 The induction coil is an L-shaped coil, and the side close to the metal thin plate is a rectangle with a size of 200mm×20mm;

[0031] 1.3 Establish an external air region wrapping the coil and the metal thin plate, and the air gap between the coil and the metal thin plate is 2mm;

[0032] Step 2: Establish a space rectangular coordinate system in this embodiment, with the geometric center of the coil as the origin of the coordinate system. Define the direction parallel to the upper surface of the thin plate and along the length direction of the coil as the x-direction of the coordinate system, the direction parallel to the upper surface of the thin plate and along the width direction of the coil as the y-direction of the coordinate system, and the direction perpendicular to the upper surface of the thin plate and outward as the z-direction of the coordinate system.

[0033] Step 3: According to the actual stationary induction heating process, perform electromagnetic-thermal coupling simulation calculation as Figure 3 shown to obtain the distribution of the heat generation rate in the steel plate within 0–10s in the space rectangular coordinate system established in Step 2, specifically including:

[0034] 3.1 Input the electromagnetic and thermal performance parameters of AH36 material varying with temperature, including magnetic permeability μ(T), electrical conductivity σ(T), thermal conductivity k(T), specific heat capacity at constant pressure Cp(T), and density ρ(T), where T is the temperature;

[0035] 3.2 Set the natural convection, thermal radiation boundary conditions on each boundary of the metal sheet and the heat conduction condition inside the metal sheet. Set an intermediate-frequency alternating current of 2000 A and 18 kHz in the coil, and the target heating duration is 10 s;

[0036] 3.3 Starting from the initial heating moment t0, first calculate the spatial distribution of electric field strength E(x, y, z, t0), magnetic field strength B(x, y, z, t0), and induced current distribution j(x, y, z, t0) in the metal sheet at t0 through Maxwell's equations. Calculate the spatial distribution of heat generation rate Q(x, y, z, t0) corresponding to the induced current distribution through Joule's law Q(x, y, z, t0) = j(x, y, z, t0) × E(x, y, z, t0). Finally, through the heat transfer formula Calculate the temperature distribution of the metal sheet at t0;

[0037] 3.4 According to the temperature distribution calculated at this moment, update the material parameters of the metal sheet after temperature change for the calculation of the spatial distribution of heat generation rate Q(x, y, z, t1) at the next calculation time step t1; Loop steps 3.3 and 3.4 until the target heating duration of 10 s is reached, and finally obtain the transient spatial distribution of heat generation rate Q(x, y, z, t) of the stationary induction heating of the thin sheet within the time period of 0 - 10 s.

[0038] Step 4: According to the transient spatial distribution of heat generation rate Q(x, y, z, t) calculated in Step 3, extract the change of heat generation rate Q(0, 0, 0, t) at the origin of the coordinate system with time as Figure 4 shown, and let the interpolation function q center (t) = Q(0, 0, 0, t).

[0039] Step 5: Respectively extract the transient change data of the heat generation rate along the x-axis, y-axis, and z-axis, as Figure 5 shown. Based on the spatial coordinate system O-xyz established in Step 2, the parameters σ l (t), l(t), σ w (t), w(t), σ d (t) in the distribution function are obtained by least squares fitting. The changes of these fitted parameters with time are as Figure 6 shown.

[0040] Step 6: According to the interpolation function q obtained by solving and fittingcenter (t), σ l (t), l(t), σ w (t), w(t), σ d (t), according to the heat source model formula q(x, y, z, t) = q center (t) × f(x, t) × g(y, t) × h(z, t), an equivalent heat source model with the heating center position as the coordinate origin is established, where:

[0041] Step 7: Establish a local coordinate system o-xyz at the center position of the thin plate of the same size. The origin of this coordinate system is the upper surface of the thin plate corresponding to the heating center point. The direction parallel to the upper surface of the thin plate and along the length direction of the expected heating coil is defined as the x-direction of the coordinate system, the direction parallel to the upper surface of the thin plate and along the width direction of the expected heating coil is defined as the y-direction of the coordinate system, the direction perpendicular to the upper surface of the thin plate and outward is defined as the z-direction of the coordinate system. Apply the equivalent heat source model established in Step 6 to this local coordinate system for transient temperature field calculation.

[0042] As Figure 7 shown, compare the temperatures at the center point directly below the coil (the origin O of the space coordinate system) obtained from the experimental test, the electromagnetic-thermal transient two-way coupling simulation carried out in Step 3, and the equivalent heat source simulation proposed by the present invention. The temperature change curves of the three are basically the same, which fully shows that the equivalent heat source simulation carried out by this method has high accuracy.

[0043] As shown in Table 1, compare the calculation time required for the electromagnetic-thermal transient two-way coupling simulation carried out in Step 3 and the equivalent heat source simulation proposed by the present invention. The results show that the transient equivalent heat source simulation method for stationary induction heating of thin plates proposed by the present invention can avoid complex and time-consuming electromagnetic field analysis and greatly reduce the calculation time of thin plate induction heating forming simulation.

[0044] Table 1 Simulation method Electromagnetic-thermal transient bidirectional coupling method Equivalent heat source method Computation time 42 h 18 min 17 min 21 s

[0045] Step 8: Apply the established equivalent heat source model to the calculation of multi-step induction heating of large-size plates. The schematic diagram of the temperature field and the final induction heating deformation calculation is as Figure 8 shown. The size of this thin plate component is 1000mm × 600mm × 6mm, and a total of 3 columns and 12 times of induction heating bending forming are carried out. That is, 12 local coordinate systems need to be defined with the center positions of the 12 times of heating as the coordinate origins, and the transient equivalent heat source model is applied. As Figure 8As shown, the sheet metal generates a hyperbolic deformation after heating, which meets the expectations of the bending process. If the traditional electromagnetic-thermal transient two-way coupling calculation method is used, the calculation time requires nearly 20 days. However, by using the equivalent heat source simulation method proposed in the present invention, the calculation work can be completed in only one day, and the simulation results are reasonable and the accuracy is high.

[0046] Those skilled in the art can make local adjustments to the above specific implementation in different ways without departing from the principles and purposes of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific implementation. All implementation solutions within its scope are subject to the present invention.

Claims

1. A transient equivalent heat source simulation method for stationary induction heating of thin plates, characterized in that, According to the actual working conditions of stationary induction heating of thin plates, a spatial rectangular coordinate system and a corresponding electromagnetic-thermal transient bidirectional coupling simulation model are established. Furthermore, the transient spatial distribution of the heat generation rate in this spatial rectangular coordinate system is calculated and the transient spatial distribution function of the heat generation rate is fitted. Then, local rectangular coordinate systems are established at each heating position of the thin plate to be processed, and the transient spatial distribution function of the heat generation rate is applied to each local rectangular coordinate system and thermal-structural coupling calculations are performed to realize the deformation prediction of large thin plate components.

2. The transient equivalent heat source simulation method for stationary induction heating of thin plates according to claim 1, characterized in that The described spatial rectangular coordinate system means that: taking the geometric center of the coil as the origin of the coordinate system, the direction parallel to the upper surface of the thin plate and along the length direction of the coil is defined as the x-direction of the coordinate system, the direction parallel to the upper surface of the thin plate and along the width direction of the coil is defined as the y-direction of the coordinate system, and the direction perpendicular to the upper surface of the thin plate and outward is defined as the z-direction of the coordinate system.

3. The transient equivalent heat source simulation method for static induction heating of thin plates according to claim 1, characterized in that, The electromagnetic-thermal transient bidirectional coupling simulation model is established through finite element analysis software. Specifically: a) Establish a geometric model of stationary induction heating of thin plates including induction coils, metal thin plates, and air gaps; b) Input the electromagnetic and thermal performance parameters of the metal thin plate that vary with temperature; c) Input the heat convection, heat radiation boundary conditions and alternating current parameters in the coil that conform to the actual working conditions; d) For each calculation time step, first calculate the spatial distribution of the electromagnetic field within this time step through Maxwell's equations. After calculating the induced current in the metal thin plate, calculate the spatial distribution of the heat generation rate corresponding to the induced current distribution through Joule's law, and calculate the current temperature distribution of the metal thin plate through heat transfer formulas; e) According to the temperature distribution calculated in step d, update the material parameters of the metal thin plate after temperature change for the calculation of the next calculation time step; loop through steps d - e until the target heating time is reached, and finally obtain the transient spatial distribution of the heat generation rate of stationary induction heating of thin plates during the heating period.

4. The transient equivalent heat source simulation method for static induction heating of thin plates according to claim 1, characterized in that, The transient spatial distribution of the heat generation rate refers to: the Joule heat generated by the induced current per unit volume in the metal thin plate per unit time, with the unit of W / m 3 ; The transient spatial distribution function of the heat generation rate q(x, y, z, t) = q center (t) × f(x, t) × g(y, t) × h(z, t), where: q center (t) is the transient heat generation rate calculated at the surface of the thin plate directly below the center of the coil in the electromagnetic-thermal transient bidirectional coupling simulation model, and it is an interpolation function with time as the independent variable; the distribution function of the heat generation rate in the x direction The distribution function of the heat generation rate in the y direction The distribution function of the heat generation rate in the z direction where: x, y, z are the coordinates in the said rectangular space coordinate system, σ l (t), l(t) is the shape parameter in the length direction of the coil, σ w (t), w(t) is the shape parameter in the width direction of the coil, σ d (t) is the heating penetration depth parameter, t is the time, and the above shape parameters are all interpolation functions with time as the independent variable, obtained by fitting the transient spatial distribution data of the heat generation rate in the electromagnetic-thermal bidirectional coupling simulation model.

5. The transient equivalent heat source simulation method for static induction heating of thin plates according to claim 1, characterized in that The local rectangular coordinate system established at each heating position of the large thin plate component means that: taking the geometric center of the coil during heating at this position as the origin of the coordinate system, the direction parallel to the upper surface of the thin plate and along the length direction of the coil is defined as the x-direction of the coordinate system, the direction parallel to the upper surface of the thin plate and along the width direction of the coil is defined as the y-direction of the coordinate system, and the direction perpendicular to the upper surface of the thin plate and outward is defined as the z-direction of the coordinate system.

6. The transient equivalent heat source simulation method for static induction heating of thin plates according to claim 1, characterized in that The described fitting specifically includes: Step 1: Input the magnetic permeability μ(T), electrical conductivity σ(T), thermal conductivity k(T), specific heat capacity at constant pressure Cp(T), and density ρ(T) of the material that vary with temperature, where T is the temperature; Step 2: Set the natural convection, heat radiation boundary conditions on each boundary of the metal thin plate and the heat conduction conditions inside the metal thin plate; Step 3: Starting from the initial heating moment t0, first calculate the spatial distribution of the electric field strength E(x, y, z, t0), the spatial distribution of the magnetic field strength B(x, y, z, t0), and the induced current distribution j(x, y, z, t0) within the metal sheet at the moment t0 through Maxwell's equations. Calculate the spatial distribution of the heat generation rate Q(x, y, z, t0) corresponding to the induced current distribution through Joule's law Q(x, y, z, t0) = j(x, y, z, t0) × E(x, y, z, t0). Finally, through the heat transfer formula calculate the temperature distribution of the metal sheet at the moment t0; Step 4: According to the temperature distribution calculated at this moment, update the material parameters of the metal thin plate after temperature change for the calculation of the spatial distribution of the heat generation rate Q(x, y, z, t1) at the next calculation time step t1; loop through step 3 and step 4 until the target heating duration is reached, and finally obtain the transient spatial distribution of the heat generation rate Q(x, y, z, t) of stationary induction heating of thin plates during the period.

7. A transient equivalent heat source simulation system for stationary induction heating of thin plates implementing the method described in any one of claims 1-6, characterized in that, including: Electromagnetic-thermal transient bidirectional coupling calculation unit, heat generation rate data extraction unit, heat generation rate spatial distribution function fitting unit, and equivalent heat source model application unit, where: The electromagnetic-thermal transient bidirectional coupling calculation unit establishes an electromagnetic-thermal transient bidirectional coupling calculation model according to the electromagnetic induction heating process of the actual metal thin plate and conducts simulation calculations; The heat generation rate data extraction unit extracts the transient spatial distribution data of the heat generation rate in the metal thin plate according to the electromagnetic-thermal transient bidirectional coupling calculation results; The heat generation rate spatial distribution function fitting unit obtains the transient spatial distribution function of the heat generation rate through data fitting according to the extracted transient spatial distribution data of the heat generation rate; The equivalent heat source model application unit establishes a corresponding local rectangular coordinate system according to the heating position of the induction heating process of the large thin plate component, and applies the transient spatial distribution function of the heat generation rate to the corresponding local rectangular coordinate system according to the construction sequence.

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